Sarin: Invisible and deadly

(CNN)Clear, colorless, tasteless, odorless and deadly. Sarin -- which weapons inspectors say has been used in chemical attacks in Syria -- is a poisonous liquid that can easily evaporate and change to gas, rapidly spreading throughout the immediate environment.

It's classified as a "nerve agent," which is defined by the US Centers for Disease Control and Prevention as "the most toxic and rapidly acting of the known chemical warfare agents."
Nerve agents work like insect-killing insecticides, the CDC says. But they're much more potent.
Although it dissipates quickly, sarin presents a short-lived threat through skin contact, eye contact, or inhalation. Mild or moderately exposed people often recover completely, while those who are severely exposed to sarin are not likely to survive.
Nerve agents disable an enzyme that the body uses as a kind of "off switch" for glands and muscles, according to the CDC website: "Without an 'off switch,' the glands and muscles are constantly being stimulated. Exposed people may become tired and no longer be able to keep breathing."
    During the 1990s, terrorists used sarin in Japan for attacks in public places. Syria's military was first accused in 2013 of using sarin to attack civilians, including children.
    The 1993 Chemical Weapons Convention arms control treaty, signed by more than 160 nations including Syria, made producing and storing sarin illegal in 1997.
    Here's a brief time line of this frightening, invisible killer:


    Sarin is developed in Germany as a pesticide.

    April-May 1967

    The US military secretly tests sarin in the Upper Waiakea Forest Reserve on the island of Hawaii. The testers detonate sarin-filled 155mm artillery shells to study how the nerve agent disperses in a tropical jungle. The Pentagon confirms the "Red Oak" program in November 2002.


    Sarin and other nerve agents may have been used in chemical warfare during the Iran-Iraq War.

    March 1988

    On "Bloody Friday," the Iraqi air force attacks the northern Iraq town of Halabja with poisonous gases that were thought to include sarin, VX and other deadly compounds. Reports indicate that 5,000 people die in the attack. Countless others suffer eyesight loss, respiratory ailments and cancers.

    June 27, 1994

    In Japan, seven people die and more than 500 are hospitalized when the Aum Supreme Truth (or Aum Shinri Kyo) cult releases sarin from a truck by driving slowly around an apartment complex in Matsumoto, Nagano Prefecture. Another victim dies in 2008.

    March 20, 1995

    The Aum Supreme Truth cult, now known as Aleph, places plastic bags of sarin on trains that converge in the Tokyo government district during rush hour. Thirteen people die and more than 5,000 become ill.

    May 17, 2004

    A coalition convoy in Baghdad finds sarin gas in an artillery round that had been rigged as an improvised explosive device. The IED detonates as officials attempt to defuse it. Two members of the explosive ordinance team suffer minor exposure.

    June 23, 2006

    The US Army releases a report to Congress stating that allied forces have recovered approximately 500 munitions containing degraded mustard or sarin gas since 2003. The weapons were produced before the 1991 Gulf War and many experts believe the sarin would no longer be dangerous.

    June 15, 2012

    Katsuya Takahashi, 54, the last fugitive suspect in the 1995 sarin attacks on the Tokyo subway, is captured by Japanese police, ending a 17-year manhunt.

    April 25, 2013

    Then-Defense Secretary Chuck Hagel announces that Syria has used sarin on a small scale, killing 150 people in the country.

    August 21, 2013

    A new alleged chemical weapons attack kills more than 1,000 people in the Syrian countryside outside its capital, Damascus. Hundreds of those killed are children.

    September 1, 2013

    Then-US Secretary of State John Kerry announces that samples of blood and hair taken from eastern Damascus have "tested positive for signatures of sarin."

    September 16, 2013

    United Nations weapons inspectors return "overwhelming and indisputable" evidence of the use of sarin in Syria, Secretary-General Ban Ki-moon says, calling the findings "beyond doubt and beyond the pale." Read the report.

    January 4, 2016

    The UN releases a report that indicates Syrians may have been exposed to a sarin-type gas in 11 instances. The UN bases its report on a publication by the Organization for the Prohibition of Chemical Weapons (OPCW). Source of the gas and those responsible for its use are being investigated.

    April 4, 2017

    An airstrike on a rebel-held town in northwestern Syria leaves 89 civilians dead, including children, from a suspected chemical attack, using sarin gas. The US, Turkey and other Western states blame the regime of Syrian President Bashar al-Assad, who vehemently denies the accusation. The following week, UK scientists claim to have evidence that sarin gas, or a similar substance, was used based on samples tested from victims. Investigations continue to confirm the gas used and those responsible.

    April 26, 2017

    French Foreign Minister Jean-Marc Ayrault announces that samples taken from the attack on the rebel-held town of Khan Sheikhoun matched those from a previous incident, and that the evidence provides proof that the Syrian regime is responsible for carrying out the attack on April 4.